The present invention relates to a diagnosis method of deterioration of insulators such as rubber or plastic electric power cables, which diagnoses accurately the deterioration without a particular countermeasures for harmonics in an electric power source equipment for the test.
In the prior art, the diagnosis of the deterioration is that which applies the alternative voltage of commercial supply frequency to the electric power cables (in the following, called cables) insulated by the rubber or plastic and measures loss current components contained in current flowing in a ground conductor. In this case, the deterioration of the insulation is diagnosed by examining a third harmonic component contained in the loss current.
There are the following problems in the above mentioned prior art diagnoses of the deterioration.
(1) When the harmonics contained in the applied voltage waves are suppressed thoroughly, the deterioration diagnoses by examining the third harmonic in the conventional method can be performed precisely. But, when harmonics, particularly the third harmonic, are contained in the applied waves, the harmonics in the applied wave are respectively contained in the detected loss current. Since these harmonic signals in the loss current are squared by the harmonic degree other than the original one, for example, the third harmonic is magnified nine times compared to the original harmonic in the applied wave and this magnified third harmonic is contained in the waves of the loss current as noise. Consequently, the precise deterioration diagnosis by examining the third harmonic in the loss current cannot be performed.
Using a power supply in which harmonics are suppressed thoroughly is good for the countermeasures, but, for realizing the power supply which the containing ratio of the harmonics is reduced, connecting filters to high voltage part of a test circuit, using a transformer having inner structures contrived so as to be difficult to occur the harmonics, or using sign wave generator suppressing the containing rate of the harmonics are necessary for an original power supply. So, realizing them is high cost, and the size of the test equipment becomes pretty large, so that it causes a problem that the implementation of the test is difficult.
(2) In prior art, many diagnosis technique under out of hot line, which diagnoses by applying an alternative voltage, all cases proposed in the prior art are carried out under the same voltage value to the operating voltage to ground of the cable. In these prior art techniques, the alternative voltage is applied usually from a test transformer for applying the alternative voltage.
The voltage to ground is 19.1 kV for a line of 33 kV, and 38.1 kV for a line of 66 kV, so that a great electrostatic capacity transformer is necessary for applying such a high voltage to long distance cable in actual power system. The generating voltage of the transformer is not so high, but the capacitance of the object line for applying the voltage is great, so there is a problem that the weight of the set equipment is very great.
For example, a transformer of 20 kV designed for a line of the electrostatic capacitance of 2.5 xcexcF and the applied voltage of 19.1 kV has a gross weight over 5 tons.
Generally many electric power cable lines are constructed under grounds of an over crowding city, so there are cases that setting the large equipment for the test is difficult.
Further, in the case that the cables are used in the underground power transmission lines, those of which structures of the terminal ends connection parts are connected directly to a gas insulated switches (GIS) are used usually. The high pressure parts therein is contained in a package insulated by the gas of sulfur six fluoride (SF6) which is good for the insulation.
So, there are not usually exposed high voltage parts in an underground room of building where a transformer substation is settled, apparatuses are settled without considering the distance for insulation thereof, and it makes the transformer substation size itself small.
On the other hand, it obstructs applying externally the voltage to cables for the test. there is not any exposed part of the high voltage, so that, when the voltage is applied to the end terminal of the connection part of the cable, very complex procedures are necessary, such as that SF6 gas in the GIS is retrieved once, and an adapter for applying the voltage for the test is attached, the SF6 gas again is filled, the test is implemented, further, after finishing the test, the gas is again retrieved to detach the adapter for applying the voltage, and GIS is returned.
It needs not only long time but also costs. Generally a million yen are necessary for one diagnosis of the deterioration, and the foregoing gas treatment of the GIS is necessary for the same costs. That is, the same supplementary costs with the essential measurement is caused, so that it brings extremely bad economics.
For resolving the forgoing problems, the applying voltage for the cable is lowered. By this, the capacity of the transformer becomes small, and the small sizing of the transformer is achieved. But, the deterioration signal becomes small by the lowering the test voltage, so that a problem aggravating the sensitivity to detect the deterioration is caused.
Like this, the prior art has problems such that the transformer for the test is big size, the inconvenience for using in a city and necessity of an enormous cost in the execution, and the necessity of the costs of the gas treatment which is necessary for applying the voltage to the GIS line. When the equipment is miniaturized by lowering the test voltage, the sensitivity of the detection signal is deteriorated, and the practicality is lost.
The present invention is developed based on the consideration of the above mentioned problem (1),(2). A first object of the present invention is that which provides the diagnosing method of the deterioration of electric power cables which can diagnose the deterioration without taking an especial countermeasure for the harmonics in the test power supply equipment.
The second object of the present invention is that which provides the diagnosing method of the deterioration of electric power cables which has a sensitivity of the signals detection having a practical level and can reduce a lot of total costs for diagnosing the deterioration.
The above mentioned problems are resolved by following components.
(1) When a first voltage of frequency f1 and a second voltage V2 of frequency f2 (V1xe2x89xa7V2) are superimposed on electric power cables, loss current components which capacitive components of frequency f1 contained in the current in a insulator of the electric power cable is rejected are measured, the current and frequency components contained in the current are investigated, and the deterioration diagnosis is executed by the components excepting the frequency components f1, frequency components f2 and the third harmonic contained thereof.
(2) In the (1), the diagnosis is implemented based frequency component of f2+2xc3x97f1 or |f2xe2x88x922xc3x97f1| contained in the loss current.
(3) In the (1) or (2), a combination that frequency f2 is two times of the frequency f1 is used as a combination of f1 and f2 of the two kinds of the alternative voltage.
(4) In the (1) or (2), as combination that f2 is 1/n times of f1 (n is integer over 3) is used as a combination of the f1 and f2.
(5) In the (3), from the frequency components contained in the loss current, a current components of 4 times of the first frequency is measured, and a phase of the voltage of the frequency of 2 times frequency to the first voltage being changed, change of the amplitude of the current components of 4 times of the first frequency is measured to diagnose the deterioration of the cable.
(6) In the (3), from the frequency components contained in the loss current, a current components of 4 times of the first frequency is measured, based on a relation a superimposed phase xcex8v2 of the second voltage V2 to the first voltage V1 and a superimposed phase xcex84 of the fourth harmonic components contained in the measured loss current to the first voltage v1, the deterioration of the cable is diagnosed.
(7) In the (6), using that a relation the superimposed phase xcex8v2 of the second voltage v2 to the first voltage v1 and a superimposed phase xcex84 of the fourth harmonic components to the first voltage v1 is approximated to a line having a constant inclination decided by the degree of the deterioration, the degree of the deterioration of the electric power cable is diagnosed based on the superimposed phase xcex84 of the fourth harmonic measured by a superimposed voltage and the superimposed phase xcex8v2 of the second voltage at the time.
(8) In the (3), the degree of the deterioration of the cable is diagnosed by estimating together both of the amplitude I4 of current components of the fourth harmonic contained in the loss current and the superimposed phase xcex84 of the current component of the fourth harmonic to the first voltage V1.
(9) In (3), keeping the rate of the first voltage V1 and second voltage V2 same, the measurement is implemented at least by two kinds of voltages, the degree of the deterioration is diagnosed by estimating the voltage characteristic of the amplitude I4 of the current components of the fourth harmonic, and the voltage characteristic of the superimposed phase xcex84 to the first voltage V1 of the current components of the fourth harmonic.
(10) In the (1),(2),(3),(4),(5),(6),(7),(8) and (9), after a first voltage V1 of frequency f1 is applied to the electric power cable, loss current components, which the capacitive components of frequency f1 contained in the current in the electric power cable is rejected, are measured, the current wave forms and frequency components contained in the current are investigated, next, fixing the first voltage same, the loss current components in the case further superimposing the second voltage V2 (V1xe2x89xa7V2) of the frequency f2, and investigating the current wave forms and the frequency components contained in the currents, the diagnosis of the deterioration is executed by the components excepting the frequency components f1, frequency components f2 and the third harmonic contained thereof.
(11) In the (1),(2),(3),(4),(5),(6),(7),(8) and (9), when a first voltage V1 of frequency f1 is applied to the electric power cable, the loss current components, which capacitive components of frequency f1 in the electric power cable are rejected, are measured, next, keeping still the operation rejecting the above mentioned capacity components, and measuring the loss current components in the case that a composed voltage of the second voltage V2 (V1xe2x89xa7V2) of the frequency f2 to the same voltage with the first voltage of frequency f1 is applied instead of the first voltage V1 of frequency f1 is measured, the current and frequency components contained in the current is investigated, and the deterioration is diagnosis by the frequency components excepting the frequency components f1, frequency components f2 and the third harmonic contained thereof in both of loss current.
(12) In the (1),(2),(3),(4),(5),(6),(7),(8),(9),(10) and (11), the first voltage V1 is commercial supply frequency.
As mentioned above, when a first voltage V1 of frequency f1 and a second voltage V2 of frequency f2 (V1xe2x89xa7V2) are superimposed on electric power cables, loss current components which capacitive components of frequency f1 from the current in the electric power cable is rejected are measured, the current component and frequency components contained in the current are investigated, and the deterioration diagnosis is executed by the components excepting the frequency components f1, frequency components f2 and the third harmonic contained thereof, by this, the deterioration of cables is precisely diagnosed without affection of the third harmonic in a power supply. Also selecting the frequency f1 and f2, the high exactitude diagnosis of the deterioration of cables is implemented.
Further, a deterioration diagnosis, having a necessary and sufficient signals detecting sensitivity, is implemented by using a widely usable and portable test equipment, so that the diagnosis of the deterioration which is good working on site and good maneuverability is realized.